Auxiliary camera break-in for television transmission systems



AUXILIARY CAMERA BREAK-IN FOR TELEVISION TRANSMISSION SYSTEMS Filed Oct.29, 1949 Feb. 12, 1952 E. s. PURINGTON ET AL 2 SHEETSSHEET 2 & mi U23 11RN! 5 mm. D .J V wwymfi FM. N mt m r BEN W1 m2 0 I zw m owe; o2 \\mmoEPE l 29 2% mu2 u mujomhzoo 26+ u o N- dumomT 23o muZ u I 3 m 0 m u u Ad mfi Mm:

om 5TH Gttorneg Patented Feb. 12, 1952 AUXILIARY CAMERA BREAK-IN FORTELE- VISION TRANSMISSION SYSTEMS Ellison S. Purington and John HaysHammond, Jr., Gloucester, Mass.; said Purington assignor to saidHammond, Jr.

Application October 29, 1949, Serial No. 124,419

7 Claims.

This invention relates to television transmitter circuits and moreespecially to circuits for putting a special picture on the videochanneltogether with a special audio tonal signal, to co-operate with aspecial receiving picture recorder.

Various other purposes will be apparent from the following descriptiontaken in connection with the accompanying drawings in which a specificembodiment has been set forth for the purposes of illustration.

In the drawings:

Fig. l is a schematic diagram showing a system for inserting the specialaudio and video transmissions automatically into the line between thestudio and the transmitter;

Fig. 2 is a diagram showing the timing relations between different audioand video transmissions, and

Fig. 3 is a schematic diagram showing a system for controlling thespecial audio and video transmissions at any desired time by the stationpersonnel.

Copending application Serial No. 124,418, filed October 29, 1949,discloses a camera and receiving system for recording the transmittedpictures, and copending application Serial No. 129,951, filed November29, 1949, describes methods of controlling and switching the operationof said camera and receiving equipment.

In Fig. 1, the special equipment is shown as provided with inputterminals ID to I! and output terminals, I8 to 23, the former beingconnected to the studio switchboard, and the latter connected to theaudio and video transmitter. Terminals H3 and I l supply a cooperatingpower for the special equipment; input terminals 12, I 3 and outputterminals 18, I9 are connected into the audio channel between theswitchboard and transmitter; input terminals l4, l5 and output terminals20, 2| are connected into the video channel between the switchboard andtransmitter; and input terminals I6, I! and output terminals 22, 23 areconnected into a channel carrying the camera sweep synchronizingsignals. Provisions are made for connecting the special video and audiosignals into the respective channels at suitable times, for whichpurpose are provided a double-throw, double-pole, audio transfer switch24 and a similar video transfer switch 25. Normally the audio input andoutput terminals are through connected, similarly the video input andoutput terminals are through connected. But when the switches 24 and 25are individually actuated in accordance with an 6 trical timing system,the special audio and video transmissions are substituted for the normaltransmissions until the switches are subsequently released. The roughtiming is effected by a synchronous motor 26 operating as a time clock,but the fine timing necessary to co-ordinate the transmitter andreceiver operations is accomplished by electronic methods using RC delaycircuits, which together with the special audio generator and thetransfer switches 24 and 25 are powerized from a power supply 21 whichsupplies also the filament power for electronic tubes.

The special video signal is produced by a television pickup camera 28,which prior to and during the transmission of the special signal isscanning the special picture material 29, and is powerized by a camerapower supply 30. As previously described the special audio and videotransmissions are cut into the circuit to pass to the transmitter onlyon closure of switches 24 and 25.

The synchronous motor 28 with input permanently connected to the A. C.power input terminals I9, I I drives through a reducing gear 3|, two

shafts 32 and 33, the shaft 32 turning a timing disc 34 at onerevolution per minute, and the shaft 33 turning two timing discs 35 and36 both at one revolution in fifteen minutes. This arrangement is forthe purpose of providing one special transmission every quarter of anhour, with accurate timing. These discs are provided with contact makingarms 31, 38, 39 carrying insulating rollers 40, 4|, 42 respectivelywhich rise and fall with the variation in cutting of the discs, andengage fixed contacts 43, 44, 45 respectively. The arms are gravityoperated, and the discs are so cut that for example contact between arm31 and contact 43 is made from 2 seconds before the start of each minuteto two seconds after, contact between arm 38 and contact 44 is made from30 seconds before to 30 seconds after the start of each fifteen minuteperiod, and contact between arm 39 and contact 45 is made from 3 minutesbefore to one minute after the start of each fifteen minute period.Conditions are depicted for example at about five seconds before theexact quarter hour. Zero reference time is taken as that for which thetransmitter will commence to control the receiver, occuringapproximately in the middle of the audio signal transmission, andpreferably at ,the exact quarter hour. ditions depicted are at zeroreference time minus five seconds.

Disc 36 is for controlling the power supplies Therefore the con- 21 and30 for the special circuits, using an A. C. relay 46 with one end of itswinding 41 connected to the contact 45 and the other end to A. C.terminal The arm 39 is connected to the A. C. terminal H, so that therelay 45 is energized from 3 minutes before zero reference time to oneminute after. Terminal I is direct connected to input power. terminalslowland b .of the power supplies 2! and 30, the relay armature 4B isconnected to terminal I I, and normally is held; open by a spring 49.

10 Front .contact,,50 .is con-:

nected to a bus 5| so that when the relay. is

closed, line H is connected through the relay contacts to bus 5| and tothe power. supply in put terminals 5i a and 5"). At the-endof-'nea)rly:- three minutes, it is assumed all electronic circuitssupplied by these power packs fl and are warmed up and ready to operateelectroni cally.

Discs 34 and 35 provide for closure of a circuit from two seconds beforeto two seconds after the.

zero reference time,.which is approximately the length of the audiocontrol signal that is sent out by the transmitter. Contact fromiarm-31:1:0 V

43 is made once a minute, contact 43:is perma nently connected to arm38, contact from arm 38 to contact 44 is made only during that minute ofthe quarter hour period inwhich it is desired to operate the circuit. Bythe series'connection of the two sets'of contactsrircuit from arm 31camera terminals !6gz and Ho This line car.-

s s 'na ff ain ainin srn hrqn u era, tion of the camera sweep circuitsand it will be understood that the synchronizing pulses for transmissiontoethe reeeiver maybe sent to the p transmitter by other channels andthese prop:

erly mig ed with the video signals and theD. C, videocomponent. Thecamera scans thepicturesheet 29 to produce the special video signals,and if desired the horizontal or, verticalsweep of the, cameramay bedifferent from standard cameras. such I that the wrii .t en. or printedmatter 00119- verted into yideo signals will be reversed and not.readable on a receiving television screen except by use of a mirror orotheruimage. reversing ,de-.-.. vice. 4 These I video 1 signals appear 7at the camera output terminals 58 59 both before, 7 during and b afterthe operation of the video transierswitch 25, v For producing the audiotone and timing the relative occurrences of the various audio and.vvideo transmissions and for. operating the Taudio and videotransferswitches, there is provided an, electronic circuit withfourtriode tubes 50, 5| 62, K 63 in orderof their first functioning. Thefila-, mentsof these tu bes are preheated from power. supply-21 which asabove described is energized about three minutes before use, inaccordance with the operation oftiming disc 36and associ-- atedcircuits. Plate power supply is turnedon for the tubes about two,seconds before zero EiQlQQQQ 'erates, All circ uits are automaticallyreset at plus 2.9 seconds when operation of disc. 34 breaks, the circuitthrough relay winding 64, deenergizi p itealiWinnin rel y 15.99 -.1 at

and theothertogroundline 56.

time through the conjoint operation of timing discs 34 and 35 andassociated circuits. For this purpose arm 31 is connected to ground line56 and therefore to the negative terminal 53 of the high voltage powersupply, contact 43 is connected to arm 38 and contact 44 is connected tooneendof the winding 64 0f a relay65, the other endflof which isconnectedto armature 56 and the positive high voltage terminal 52. Thearmature BB is normally held away from the relay front.contaot5'lqbyaspring 68. When the contactscontrolled by discs 34 and 35 are bothclosed, current passes from the positive terminal 52 through the relaywinding 64 and the disc con .tacts-to-thanegative terminal 53 of thepower tive high voltageline-69 which immediately op-- crates the audiotransfer switch 24, one end of the windinglU-of which is connected toline 69 At the same time the tube 60 operates immediately as an audiooscillator. By the conjoint action of tube 60 and switch 24, the audiooutput terminals I8, I 9 cease tobe energized by the program audio 1signals applied at input terminals l2, l3 and are energized by whateversignal is produced by the oscillator 60. This is for examplethe tonalfrecycles at ,preci s ely zero ref erenc e time. When the third tube 52operates at say plus 0.8 sec-,

ond, the video switch 25 is actuated but is released at plus 1.2 secondwhenthe fourth tube 63 0D- volved in operation: of tube 60, and a frontcontactJLinvol'ved in thetiming of tube 62 with respect to tube Bl. Thearmature 15 normally held open: to connect with back contact [Ii-by aSpring- 16, is connected to the operative high;

1 voltage line' B9.

Theoscillatoptriode 50 has its plateconductively -connected to line 69thru the oscillator coil 11 shuntedbycapacitorl8, and the plateisalsoconnectedlthrou hcapacito1 19 to the back contact 13, whichin turnis operatively connected to line fifliwhen therelay H is open. Thecoil-11 is suitablycoupled to a feedback coil with the secondandl fourthterminals 82 and 84 connected respectively to ground and-;to the grid oftriode 60, while=thefirst and third terminals 8| and B3 lations .andwith suitable circuit constants the frequency of oscillation isdetermined by the inductance of coil 11 and the shunting capacitance,whichisthatof capacitor 18 paralleled by caof capacitor 18 alone whenrelay H is closed thereby'breaking the back contact 13.

By suitable design the frequency in the former condition is made to befor example 6500 cycles and in the latter condition is made to be forexample 7000 cycles. The audio line into which terminals I2 and I3 andterminals I8 and I9 are connected is of the balanced type. The taps BIand 83 are so chosen as to develop equal but oppositely phased voltagesbetween the two contacts 85 and 86 and ground. Input terminals I2 and I3energized by the program audio signals are connected to the backcontacts 89 and 90 of the audio transfer switch 24, and the movingblades 9|, 92 actuated by the coil 10 but normally held to the backcontacts by aspring 93 are connected to the audio output line terminalsI8 and I9. During the interval of four seconds when there is voltagebetween high voltage line 69 and ground line 56, the switch blades ofswitch 24 are thrown to the left, operatively connecting by the frontcontacts the oscillator output terminals 8| and 83 to the output lineterminals I8 and I9. At other times the program input terminal I2, I3are connected through the back contacts of switch 24 to the output audioterminals I8 and I9.

For providing a suitable delay, say 2 seconds between the closure ofrelay 65, which throws the audio transfer switch and starts the audiooscillations and the closure of relay H which change the frequency ofoscillations from 6500 cycles to 1000 cycles, the contact 61 isconnected through a resistor 94 to one terminal of capacitor 95, whichin turn is connected through resistor 96 to the grid of tube 6|, whichin turn is connected to the ground line 56 through resistor 91, to whichground line the other end of capacitor 95 is also connected. Theoperative high voltage lead 69 is connected through resistor 98 to thecathode of tube 6I, which is connected to ground through resistor 99.The line 69 is also connected through the winding 12 of the relay H tothe plate of tube 6| as has been previously described.

When the relay 65 closes to establish a high voltage supply for tube 6|,the grid of tube 6| is initially at ground potential, but the cathode ispositive due to the current from line 69 through resistors 98 and 99with constants so chosen that the tube 6| is near or beyond cutoff sothat initially little or no current flows through the winding 12 ofrelay 1I. As the capacitor 95 charges to make its ungrounded terminalpositive, the potential of the grid of tube 6| becomes positive toapproach cathode potential and the tube 6I begins to pass plate current,and at a certain value of plate current, say 4 milliamperes, the relay12 operates, breaking the connection from capacitor 19 to the line 69,and establishing connection between line 69 and contact 14. This shouldtake place when the grid potential is considerably lower than its finalvalue. Thus the constants may be chosen such that the final currentthrough the relay winding 12 is say 10 milliamperes, and the grid oftube 6| is slightly above cathode potential. With suitable design thedelay involving the choice of constants may be such that the relay 1Ioperates 2 seconds after closure of relay 65 with a high degree ofreliability. This operation of relay H occurs at zero time, which may ifdesired correspond to an accurate time signal. If the adjustments arenot perfect or the 60 cycle supply line is not exactly time regulated,it is possible to insert a continuously variable and rotatable phaseshifter in the line .to the synchronous motor, and drive it in .minals20, 2|.

accordance with the time difference between theoperation of relay 12 anda standard radio time signal, so as to maintain the timing of operationof relay 12 precisely.

For timing the operation of the video transfer switch, the triode 62 isconnected to operate a' relay I00 with winding IOI in the lead from theline 69 to the plate, and has timing control circuits I02 to I01arranged and operating similar to parts 94 to 99 associated with tube6I, so that upon closure of relay 1I associated'with tube 6|, the relayI00 will close after a suitable time delay as for example 0.8 second.The relay armature I03 normally held'o'pen by'a spring I09 is connectedto the line 69 and its back contact is not utilized. The front contactIIOis connectedto line 69 when relay I00 operates. The final tube 63similarly has a relay I I I with the winding H2 in the lead from theline 69 to" the plate of tube 63, and associated therewith are elementsII3 to' I I8 similar to elements I02 to I01 for the tube 62. When relayI00 operates, connecting contact IIO to line 69, the relay III operatesafter a suitable delay time, as for example 0.4 second. The armature II9 of relay I I I is connected to contact IIO of relay I00. The backcontact I20 of relay III against which the armature H9 is normally heldby a spring I2I is connected to one end of the winding I22 of the videotransfer switch 25, the other end of which is connected to ground line56. It is clear that current passes through the winding I22 of the videotransfer switch 25 only after closure of the armature of relay I00 andbefore closure of the armature I I9 of relay III, that is during thetime interval when the circuits II3 -to H8 are delaying the operation ofthe tube 63.

The video transfer switch 25 has two moving blades I23, I24, withback'contacts I 25, I26, and front contacts I21, I28. The contacts I25,I26 are connected to the input terminals I4, I5, carrying'the programoriginating in the studio, and

the contacts I21, I28 are connected to the ter-' minals 58, 59 carryingthe picture information produced by camera 28 from the flash picture 29.Normally the switch blades are held back to connect with the backcontacts I25, I26 by a spring I29, so that the input terminals I4, I5are connected through the switch to the output ter- But when the switchis actuated during the time interval between operations'of relays I00and III, the studio program is mo' mentarily discontinued, and theterminals 58, 59 of the camera 28 are connected to the output line avideo voltage at terminals 58 and 59 corresponding the the special flashpicture 29. Subsequently upon the joint operation of the contactsassociated with discs 34 and 35, the'relay 65 operates at time b, say 2seconds before zero reference time. This operation supplies operativehigh voltages for the tubes 60, EI, 62, 63 which operate in sequence,the first tube 60 operating immediately to produce an audio tone of say6500 cycles until the next tube 6| operates. Also the audio transferswitch 34 is thrown immediately to break steamer the studiozaudiosp fimmlandisu'b stitute: the \tone developedbyvtlrewoscillatom 60;.Afteiwasuitable de1ay:; -de termined-in partybychoice ,of the :ca-

pacitor 95, the tube BI passesscurrent and relay 1 I operates at: time;c, which may be zero reference timepchanging, thegaudio tonezgeneratedby :prior tube 60 to say-{7000 cycles; and starting the building;.; upofgrid 'voltagei for :therollowing tube 62-.

Onclosureofrelay I after:a suitable time delay determined .in; partby-choice of the capacitor I03 the; relay 1 I I- 1110f; yet beingactuated, the video=transfenswitch 25': isoperated to substitute thevideoasignals fromrspecial flash camera 28 scanning. thegspecial=materiala29, for the regular studio.zvideoispliogramu. This may *takeplace at time; d, :say 0.8 second aftenzero reference time. Closure ofrelay I00-:also, starts-thebuilding up of voltage forlthe grid oftube:63,,and-after a suitabletime sa-yz 0.4 second the relay IIIoperates at-timeje, say L2 secondsafter zero reference-time, therebyQpening the; circuit for the winding of the videol transfer switch andcausing the studio program-:t ;--be.resumed.r When the-circuit .of therelay ;65 is broken by opening of the contacts associated with disc 34at timej, which is two seconds afterzero reference time, the voltage toline Iifipiis discontinued, the audio, signal ceases, all

relays: 'II," I00, I I I and the transfer; switches.- 24

and; 25, are deprived of,:operating power, so that thespecial-audio-andvideo transmission is terminated andi the studiov program resumed. Atabout 56 -secon'ds;,=later the contacts of disc 34 will: againhemadewbutby this time the com tactsgof zdisc=35.will-be-broken so that the relayB"will=not be actuatedzto repeatthe special programsv Power .isalso:shutoff attime 9, about +60 seconds by thecontaotsofidisc 36, except forthesynchronous motor 25 -which continues to operate to' cut-.inraspecialgfiash fifteen minutes later. The material 29;'of,coursemaybechanged at anytime: between, operations of the equipment.

Under-some-conditions it may not be desirable to: operate the specialaudio and videocircuits absolutely independent of other programs, butunder; the control of the program operator who normally switches:the-studio circuits. Moreover-, oit. may? be desirable to send-out thespecial programqas amadjunct towsome interprogram display. or;advertising. D 5sible1in=Figw3 wherein the circuits'shown areconnected-tobe under-th'econtrol-of the program operatorrfrom-whose=console two lines are connected, namely thewfsynchronizingl line and thestart ;line, and-uto whosezconsole two lines are connected, namely thevideo line I32 and the audioline I33; The sync line I30 comes to adual-rcamerasystem- I341- with two-cameras 135T and-i36 theforming'sca-nning material I3! pertaining, to a =paid commercialandvthe--latter scanningtheflash picture I38, if desired using a prism I39 orother imagexposition reversing device: Thus the material I 3'I- may be;of ,value I to all television receiver; observers, whilex-that'of I38-may=beof interestonly ;to;.those equipped with video recording devices:Theoutput video line I32 rgo eswbaek to the-console. The camera system;I34 is connectedto-a camera controllerIG by which the :camera'ispowerizedand by which.

the flashi material I38; is .inserteduinto the program atasuitable'time, relative-to an audioatone.

signal;v A timer I4I"connected"to an'A. C. power line may serve topowerize; a par-trofthe system during :theinterval; say three; minutesbefore each: quarter hour to-three minutes afterwduringwhich;theequipment maylbe used-chat it will be" Such an arrangement isunderstood the; operation ofsthel system. need: not; be exactly at thenominalrtime. Thus the A. 10..

current controlled-by the timer .I4.I- passes. over line I 52 to;Operate; the camera system 134ml", and over line I43 toa-transformer-IM- with sec.- ondary I45 connected over line I46 to' heatthe filaments; of a rectifierlfl; and a secondary 148- with anindicating lamp I55. The secondary I56= of transformer I53, with agrounded center-tap: is connectedto drive the rectifier I4! in the usualmanner immediately when'the start line is energized by :powersuch as .60cycle -alternating- This T'Will: 2 occur 1; when the: console current.-switch is thrown; also'oonnecting the "video output line----I32rtothe'-video transmitter and also connecting the audio output line I3 3-tothe audio transmitter." Thus afterthestartfline is ener'-'gized,=the-rectifier: output is filtered by'choke I51:

' v in combinationwith capacitors I5B=,:I59,-metered by voltmeter I Go-and multiplier I6I, putting'a positive high voltage on'line I62withirespect'to ground line -I521= Theplateof triode I5I is con-. nectedthrough an inductor I63 and a capacitor I54 toline lfiza'and also:through a capacitor I65 to' the; back contact I66 of a relay I61 withanarmature I68 connected to line I62= normally held in contact withbackv contact ISS -by-a spring I693,

except whennthe' winding .110 ofnthe relay which is connected betweenline I82-and the plate of tube I 50 carries sufficient current to break.the I contact. The: grid of 'triode I5I is connected to ground-line'I52 through a coilmIII suitably inductively coupled to inductor, I63-=to produceoscillations; which may be for example 6500 cycles'when the:armature I59 'is-connected to.

back contact 166," and 7000wcycles. when the armature is-pulled down bythe current in the winding l'l0.: An output coil is connected to theaudio line I'33,--and.also byibranch 1ineI'I3 tothe. camera controller440*. The cathode of triode I5I-isconnected to-ground-through resistorI14- shunted. by:capacitor- -I I 5;

. For: causingtherelay. I61 to operate at a time say 2 seconds aftertheinitialoscillation of triode -I'5I,- the cathodeof-triode I50 isconnected to line: I62 'by resistor I16 and-to-ground line I52 byresistor I11. so chosen as to bias the tube I50,-

nearyat orwbeyond 'cutoffwhenthe grid is at ground. potential: throughresistor I I8 to inputterminal I I9 of an RCtype lowpass filter, vwithresistors-I and ca-v pacitorJBI; connected between terminal ITS-andground line .I.52,-.-withan output terminal;l82 and a capaciton.I83-anda potentiometer-'IM'comnected from'terminal I82 to ground, and with aresistor I85. connecting the input and output terminals. I19 and I82.The variable arm of the.

potentiometer I at is connected through-a re-- sistorlil'fi to thegrid'of the'triode I50; Prior tooperation oftherectifier I41,the-capacitors I8I and I83-are fully discharged'so-that the grid oftriode I50 is at ground potential. As' the line IE2. is energized,charges'build up in capacitors I8I and I-83, making the output terminalI82'increase in'potentialas a function of time. The constantsu ofresistors, andrcapacitors and the setting of pO- tentiometer are somade'that the tube grid voltagerisesto 'causeoperatin'g plate current toflow through, relay. winding vI10 :ata suitable-timeand The-line I62 isconnected with suflicient precision after the energization of line I02.When this occurs the tone changes say to 7000 cycles, which is sent overthe audio line I33 to the console and thence to the receiver by radio.If a picture is desired, the receiver recorder is set up and is readyfor a picture at say one second after the start of the 7000 cycle tone.The audio signal in line I13 is impressed upon the camera controllerI40, which contains suitable selector and delay circuits such that thedual camera will continue to deliver video signals obtained by scanningobject I3! from the start of the 6500 cycle tone to about .8 secondafter the 7000 cycle tone, when it will then deliver video signals fromthe special material I38 for .4 second during which time the specialpicture will be recorded, when the camera will automatically switch backto material I31, which will be transmitted until the control operatorswitches to a different studio, thereby disconnecting the audio andvideo lines I32 and I33 from the station transmitter. It will beunderstood that the console may be arranged to give audio signalsaccompanying the video signals from material I31 except when the startline I3! is energized for synchronizing the receiver to the transmitterfor the special material I24. Thus for a fifteen second commercial, thematerial I31 could be sent for about the first seven seconds and thelast seven seconds with less than a second for the special material 138,and with only four seconds required for the synchronizing tone.

What is claimed is:

1. In a television transmitter having audio and video transmissionchannels normally carrying audio and video programs, a control signalgenerator having means for producing a pair of distinctive controlsignals, timed means interrupting said audio program and impressing saidcontrol signals in timed sequence on said audio transmission channel,video camera means including means for scanning a still picture, timedmeans synchronized with the start of transmission of said second controlsignal to interrupt the transmission of said video program and impressthe output of said video camera on said video transmission channel fortransmitting said picture a predetermined time interval after the startof said second control signal transmission, and timed means forterminating the transmission of said picture a selected time periodafter its start and restoring the transmission of said video program.

2. A transmitter as set forth in claim 1 in which 10 the signalproducing means in said control signal generator is operated to producedifferent audio tones.

3. A transmitter as set forth in claim 1 in which the timed meansimpressing the control signals in timed sequence is arranged to transmitthe first control signal for a predetermined period of time, thentransmit the second control signal for a predetermined period of timeand transmit the video picture for a shorter predetermined period oftime during the transmission of said second control signal.

4. In a, transmitter as set forth in claim 1, timed means cooperatingwith said first-named timed means initiating the transmission of saidsignals at selected intervals.

5. A transmitter, as set forth in claim 1, including electron tubes forproducing signals and for controlling switching functions, power meansfor powerizing said tubes, and means timed with respect to said controlsignals to actuate said power means for a period overlapping the controlsignal transmission periods whereby the tubes are rendered operativeduring transmission periods.

6. In a transmitter as set forth in claim 5 timed means to render saidpower means operative to powerize said tubes and manual means forcontrolling said tubes to initiate said transmissions during the periodsof actuation of said power means.

'7. A transmitter as set forth in claim 1 having means whereby saidaudio program transmission is interrupted only during the transmissionof said control signals and said video program transmission isinterrupted only during the transmission of said still picture.

ELLISON S. PURINGTON. JOHN HAYS HAMMOND, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,164,297 Bedford June 27, 19392,181,564 Goldsmith Nov. 28, 1939 2,193,869 Goldsmith Mar. 19, 19402,240,420 Schnitzer Apr. 29, 1941 2,272,043 Browne Feb. 3, 19422,314,471 Wright Mar. 23, 1943 2,402,083 Reid June 11, 1946 2,454,651Homrighous Nov. 23, 1948

